In three dimensions, the vector transformation rule is written as

where
.
In two dimensions, this transformation rule is the familiar

In matrix form,

Since we are using sines, the direction of measurement of
is required. In this case, it is measured counterclockwise.
In three dimensions, the second-order tensor transformation rule is written as

where
.
The Cauchy stress
is a symmetric second-order tensor. In two dimensions, the transformation rule for stress is then written as

In matrix form,

Since we are using sines, the direction of measurement of
is required. In this case, it is measured counterclockwise.
Let construct an orthonormal basis of the second order tensor projected in the first order tensor






The stress and strain tensors are now defined by :

and

Then once constructs the bound matrix in the orthonormal base
![{\displaystyle \left[{\hat {R}}(\theta )\right]=\left[{\begin{matrix}R_{11}^{2}&R_{12}^{2}&R_{13}^{2}&{\sqrt {2}}R_{12}R_{13}&{\sqrt {2}}R_{11}R_{13}&{\sqrt {2}}R_{11}R_{12}\\R_{21}^{2}&R_{22}^{2}&R_{23}^{2}&{\sqrt {2}}R_{22}R_{23}&{\sqrt {2}}R_{21}R_{23}&{\sqrt {2}}R_{22}R_{21}\\R_{31}^{2}&R_{32}^{2}&R_{33}^{2}&{\sqrt {2}}R_{33}R_{32}&{\sqrt {2}}R_{33}R_{31}&{\sqrt {2}}R_{31}R_{32}\\{\sqrt {2}}R_{21}R_{31}&{\sqrt {2}}R_{22}R_{32}&{\sqrt {2}}R_{23}R_{33}&R_{22}R_{33}+R_{23}R_{32}&R_{21}R_{33}+R_{31}R_{23}&R_{21}R_{32}+R_{31}R_{22}\\{\sqrt {2}}R_{11}R_{31}&{\sqrt {2}}R_{12}R_{32}&{\sqrt {2}}R_{13}R_{33}&R_{12}R_{33}+R_{32}R_{13}&R_{11}R_{33}+R_{13}R_{31}&R_{11}R_{32}+R_{31}R_{12}\\{\sqrt {2}}R_{11}R_{21}&{\sqrt {2}}R_{12}R_{22}&{\sqrt {2}}R_{13}R_{23}&R_{12}R_{23}+R_{22}R_{13}&R_{11}R_{23}+R_{21}R_{13}&R_{11}R_{22}+R_{21}R_{12}\\\end{matrix}}\right]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f56d732e51be4b9c0155cb96f2dde3f7a05a794e)
with
the rotation matrix in
base.
![{\displaystyle \left[R(\theta )\right]=\left[{\begin{matrix}1&0&0\\0&\cos \theta &\sin \theta \\0&-\sin \theta &\cos \theta \end{matrix}}\right]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/70700a390859bbb0f44c1f4d3f6f349721570777)
is the rotation along the axis
in the :
base
The associated rotation in the
base is :
![{\displaystyle \left[{\hat {R}}(\theta )\right]=\left[{\begin{matrix}1&0&0&0&0&0\\0&\cos ^{2}\theta &\sin ^{2}\theta &{\sqrt {2}}\sin \theta \cos \theta &0&0\\0&\sin ^{2}\theta &\cos ^{2}\theta &-{\sqrt {2}}\sin \theta \cos \theta &0&0\\0&-{\sqrt {2}}\sin \theta \cos \theta &{\sqrt {2}}\sin \theta \cos \theta &\cos ^{2}\theta -\sin ^{2}\theta &0&0\\0&0&0&0&\cos \theta &-\sin \theta \\0&0&0&0&\sin \theta &\cos \theta \\\end{matrix}}\right]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/d4b35e31efd57b555e6f3cf189fc8d945bb631b5)
The rotation of a second order tensor is now defined by :
![{\displaystyle \left\{\sigma (\theta )\right\}={\left[{\hat {R}}(\theta )\right]}^{T}\left\{\sigma \right\}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/be5bfe9b9683282f4801b5b4fd04c2ddcd00ad15)
The élasticity tensor
in the :
is defined in the :
by
![{\displaystyle \left[{\overline {C}}\right]=\left[{\begin{aligned}C_{1111}&C_{1122}&C_{1133}&{\sqrt {2}}C_{1123}&{\sqrt {2}}C_{1131}&{\sqrt {2}}C_{1112}\\C_{1122}&C_{2222}&C_{2233}&{\sqrt {2}}C_{2223}&{\sqrt {2}}C_{2231}&{\sqrt {2}}C_{2212}\\C_{1133}&C_{2233}&C_{3333}&{\sqrt {2}}C_{3323}&{\sqrt {2}}C_{3331}&{\sqrt {2}}C_{3312}\\{\sqrt {2}}C_{1123}&{\sqrt {2}}C_{2223}&{\sqrt {2}}C_{2333}&2C_{2323}&2C_{2331}&2C_{2312}\\{\sqrt {2}}C_{1131}&{\sqrt {2}}C_{2231}&{\sqrt {2}}C_{3331}&2C_{2331}&2C_{3131}&2C_{3112}\\{\sqrt {2}}C_{1112}&{\sqrt {2}}C_{2212}&{\sqrt {2}}C_{3312}&2C_{2312}&2C_{3112}&2C_{1212}\end{aligned}}\right]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/b1ac78ae1ece4f770b9de32708bb7bdbfeee8368)
and is rotated by:
![{\displaystyle {\left[{\overline {C}}(\theta )\right]}_{g}={\left[{\hat {R}}(\theta )\right]}^{T}\left[{\overline {C}}\right]\left[{\hat {R}}(\theta )\right]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/fd3b89d7d4363d0916ff2986a6ab1f2247f6c1cd)
Introduction to Elasticity